The transcription factor Pdx1 is expressed throughout the pancreas early, but selectively in insulin-producing cells postnatally. Previous studies showed that conserved regulatory regions, Areas I and II (Pdx1PB), directed pancreatic endocrine cell expression, while an adjacent region (Pdx1XB) containing the conserved Area III directed transient Ò cell expression. We generated transgenic mice in order to lineage trace cells in which these promoter fragments were activated: Pdx1PBCre mediated only endocrine cell recombination, while Pdx1XBCre directed broad and early recombination throughout the developing pancreas. An Areas I-II-III reporter transgene was expressed throughout the E10.5 pancreas, gradually becoming Ò cell selective, similar to endogenous Pdx1. These data suggested that sequences within Area III mediate early pancreas-wide Pdx1 expression. Area III contains a binding site for PTF1, a transcription factor complex essential for development of all pancreatic cell types. This site contributed to Area III-dependent reporter gene expression in an acinar cell line, while PTF1a specifically trans-activated an Area III-containing reporter in a non-pancreatic cell line. Importantly, Ptf1a occupied Area III of the endogenous Pdx1 promoter in E11.5 pancreatic buds. These data strongly suggest that PTF1 is an early activator of Pdx1 in pancreatic progenitor cells.
Ptf1a expression in the early pancreatic primordium requires signaling from the adjacent vascular endothelial cells, which are reciprocally sensitive to VEGF signaling from the pancreas. To elucidate the role of the VEGF signaling pathway in pancreas differentiation, we analyzed transgenic mice that express agonists selective for VEGF receptor isoforms (VEGFR1 or VEGFR2) throughout the pancreas. Morphometric analysis of antibody labeled cross-sections revealed that at postnatal day one, mice expressing the VEGFR2 agonist had a 49% increase in endothelial to endocrine ratio, but islet size was similar to wild type. In contrast, VEGFR1 agonist expression caused a decrease in endothelial to endocrine ratio, but surprisingly, islets were smaller than in wild type. Taken together, these results suggest that VEGFR1 and VEGFR2 signaling have distinct roles in pancreatic islet development, and the expansion of endocrine mass mediated by increased VEGF may require increased signaling through both receptors.
| Identifer | oai:union.ndltd.org:VANDERBILT/oai:VANDERBILTETD:etd-07272007-140331 |
| Date | 02 August 2007 |
| Creators | Wiebe, Peter O. |
| Contributors | Guoqiang Gu, David Bader, David Wasserman, Richard O'Brien, Al Powers |
| Publisher | VANDERBILT |
| Source Sets | Vanderbilt University Theses |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.library.vanderbilt.edu/available/etd-07272007-140331/ |
| Rights | unrestricted, I hereby certify that, if appropriate, I have obtained and attached hereto a written permission statement from the owner(s) of each third party copyrighted matter to be included in my thesis, dissertation, or project report, allowing distribution as specified below. I certify that the version I submitted is the same as that approved by my advisory committee. I hereby grant to Vanderbilt University or its agents the non-exclusive license to archive and make accessible, under the conditions specified below, my thesis, dissertation, or project report in whole or in part in all forms of media, now or hereafter known. I retain all other ownership rights to the copyright of the thesis, dissertation or project report. I also retain the right to use in future works (such as articles or books) all or part of this thesis, dissertation, or project report. |
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